Move kernel baseline tests to front_end.

pkg/kernel/testcases/spec-mode/external.baseline.txt

Index: pkg/kernel/testcases/spec-mode/external.baseline.txt
diff --git a/pkg/kernel/testcases/spec-mode/external.baseline.txt b/pkg/kernel/testcases/spec-mode/external.baseline.txt
deleted file mode 100644
index 74c2005687db45166e67a6179151d6a248415ab0..0000000000000000000000000000000000000000
--- a/pkg/kernel/testcases/spec-mode/external.baseline.txt
+++ /dev/null
@@ -1,16 +0,0 @@
-library;
-import self as self;
-import "dart:core" as core;
-import "dart:isolate" as iso;
-
-static field dynamic subscription = null;
-static method onData(dynamic x) → void {
-  core::print(x);
-  self::subscription.cancel();
-}
-static method main() → dynamic {
-  dynamic string = core::String::fromCharCode(65);
-  dynamic port = iso::ReceivePort::•();
-  self::subscription = port.listen(self::onData);
-  port.sendPort.send(string);
-}